Pitch, roll and drag stabilization of a tethered hydrokinetic device

ABSTRACT

A hydrokinetic device is provided that extracts power from a water current. The device comprises a buoyant body and a rotor coupled to the buoyant body configured to drive a power generator. The buoyant body and the rotor jointly define a center of buoyancy and a center of gravity, the center of buoyancy being located above and upstream of the center of gravity.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application claims priority and the benefit thereof from U.S.Provisional Application No. 61/221,676, filed on Jun. 30, 2009, andentitled OCEAN CURRENT TURBINE AND HYDROKINETIC POWER GENERATIONAPPARATUSES AND RELATED METHODS, ALONG WITH MOORING & YAW ARRANGEMENTS,FURLING ROTOR DEPTH CONTROL, AND MOORING HARNESSES FOR USE THEREWITH,the entirety of which is hereby incorporated herein by reference. Thisapplication also claims priority and the benefit thereof from U.S.Provisional Application No. 61/236,222, filed on Aug. 24, 2009, andentitled SELF-CONTAINED VARIABLE PITCH CONTROL ROTOR HUB; METHOD OFMAXIMIZING ENERGY OUTPUT AND CONTROLLING OPERATING DEPTH OF AN OCEANCURRENT TURBINE; AND VARIABLE DEPTH HYDROPLANE SLED, the entirety ofwhich is also hereby incorporated herein by reference. This applicationalso claims priority and the benefit thereof from U.S. ProvisionalApplication No. 61/328,884, filed on Apr. 28, 2010, and entitled FLOODEDANCHORING SYSTEM AND METHOD OF DEPLOYMENT, POSITIONING AND RECOVERY, theentirety of which is hereby incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to a method, a system and a device forgenerating power from the kinetic energy of a fluid current, includingpitch, roll and drag stabilization of the device. More particularly, thedisclosure relates to a method, a system and a device for generatingpower from the kinetic energy of an ocean or river current, includingpitch, roll and drag stabilization of the device.

2. Related Art

Kinetic energy of flowing ocean currents represents a significant sourceof clean renewable energy. The water in the world's oceans is constantlyin motion, and in many locations there exist repeatable, consistent andrapidly moving ocean currents with speeds in excess of 1.5meters-per-second (m/s). Such examples include the Gulf Stream, theHumboldt, the Kuroshio, the Agulhas and others. These currents havetheir origins in ocean thermal and salinity gradients, Coriolis forces,and other ocean thermal transport mechanisms.

These currents represent “rivers in the ocean” which lie predominantlyin continental shelf areas with bottom depths in excess of 300 meters.Such depths necessitate mooring the hydrokinetic device with cables ortethers to upstream anchors fixed to the sea bed. Upstream mooringcables can introduce destabilizing pitching moments onto thehydrokinetic device that require opposing moments to maintain a leveltrim steady state attitude that provides for the alignment of therotational axis of the rotor and the free stream current flow direction.Misalignment of the rotational axis and free stream current flowdirection (“furl angle”) can rapidly degrade energy conversionperformance of a horizontal axis rotor. An additional destabilizingrolling moment, or adverse torque, may be introduced by the rotation ofa horizontal axis rotor. Further, it may be advantageous to provide ameans to mimic or proxy the rotor drag force that disappears when therotor ceases operation in order to maintain depth control and to preventa surge forward in the position of the hydrokinetic device.

An upstream mooring cable tension, which has a vertical force component,referred to as the “drowning force,” acts as an apparent weight andtends to pull the hydrokinetic device to greater depths. Since it isgenerally advantageous to attach the mooring cable(s) near the nose ofthe hydrokinetic device to promote directional alignment with changes inthe free-stream current direction, the drowning force also creates anose down pitching moment referred to as the “drowning moment” and thismoment must be opposed by restoring moments generated by thehydrokinetic device. As the angle of the mooring cable with thehorizontal (mooring cable “intercept angle”) becomes steeper, thedrowning force increases, thus increasing the drowning moment andrequiring even greater restoring nose up moments to maintain a leveltrim steady state attitude for maximum energy conversion performance.

Various methods are known to oppose destabilizing pitching moments,including, for example, fore and aft hydroplane lifting surfaces, usinga lever system by changing the mooring cable attachment point or causingthe device to be semi submerged allowing a reserve of buoyancy above thewaterline to counteract the drowning moment. These known solutions tendto trade device stability for a loss in energy conversion performance byincreasing the furl angle or by creating an apparent furl angle, orwake, upstream of the rotor that drifts downstream and impinges upon therotor swept area thereby introducing a flow inclination angle into therotor swept area.

For example, in U.S. Pat. No. 7,291,936, issued to Robson, ahydrokinetic device is described that uses a leverage system, whichalters the attachment point of the upstream mooring cable, and asupplementary system, which alters the location of the center of gravityfore and aft, to provide for pitch angle changes of the entire device,thereby changing the angle of attack of an attached hydroplane wing tocreate more (or less) lift to offset changes in the drowning force, suchthat the device remains at or near a constant depth of operation. Themain axis of the rotors of the Robson device becomes furled with theoncoming flow direction by pitching the entire device nose up or nosedown to achieve constant depth operation. Robson moves the center ofgravity and alters the lever point location not to ensure alignment ofthe rotor axis with the free stream, but rather to pitch the entiredevice for constant depth operation. Robson also suggests that themooring cable intercept angle “should be kept reasonably small.” Shallowmooring cable intercept angles imply lengthy, more costly and heaviermooring cables as well as a less efficient use of the natural resourcein that a larger projected geographic area is required to deploy thesame number of devices in a regular patterned array.

U.S. Patent Application Publication No. US2008/0050993 to Mackieproposes fore and aft trimming hydrodynamic surfaces, as well as abovesurface buoyant elements, to counteract undesirable pitching moments for“near level trim to ensure optimum performance from the horizontal axismarine turbine.” Both of these solutions compromise energy conversionperformance of the horizontal axis rotor. Fore and aft trimmingsurfaces, while providing lift to create moments to maintain level trim,also create a flow downwash inclination angle, or wake, that driftsdownstream and impinges on the rotor swept area, presenting an apparentfurl angle to the rotor, thereby reducing its energy conversionperformance. Further, above-surface buoyant elements subject the deviceto wind/wave action disturbances on the surface, which translate intoperiodic or sinusoidal bobbing action of the entire device and therotor, further degrading energy conversion performance. Both Robson andMackie state that the center of buoyancy is located directly above thecenter of gravity “ensuring stability of the device,” but do not offeradditional information or teachings with respect to the relativelocations of the center of gravity and the center of buoyancy.

Significant adverse rolling moments may be introduced by the rotation ofthe rotor, since diameter and torque of the rotor tend to be of largemeasure in comparison to the remainder of the hydrokinetic device.Adverse torque is the tendency of the entire hydrokinetic device itselfto rotate in the same direction as the rotational direction of therotor, and, in the case of a horizontal axis rotor, this translates tothe presence of a rolling moment proportional to the amount of torqueabsorbed by the rotor. The hydrokinetic device may therefore present arestoring torque to counteract the adverse torque created by the rotorto remain in a preferred vertical orientation.

Known hydrokinetic devices, including those described in U.S. Pat. Nos.6,091,161 and 7,291,936 and U.S. Patent Application Publication No.2008/0018115, typically use a second rotor of equal size, but oppositedirectional rotation to provide a cancelling torque. Dual counterrotating rotors can be operationally problematic and require rotortorque synchronization, thereby reducing machine availability in theevent of the unintentional stoppage of one rotor since that necessitatesthe intentional stoppage of the second functional rotor to prevent therisk of overturning.

U.S. Pat. No. 4,025,220, and patent application publication Nos. US2007/023107 and WO 2009/004420A2 propose the use of a multi-pointmooring scheme by adding additional mooring cables attached to certainpoints on the device to provide restraining forces and moments via cabletension for maintaining proper device attitude. Given depths of severalhundred meters, additional mooring cables are lengthy, costly, increasesystem weight and provide greater entanglement risk as well asadditional maintenance concerns.

Given that the drag force created by the operational rotor is nearlyequivalent to a flat plate of equivalent swept area, the total dragforce acting on the hydrokinetic device may change by, for example,several hundred percent between a rotor operational condition and arotor non-operational condition. As a result, the upstream mooringcables may slacken to a catenary condition, causing the hydrokineticdevice to surge forward in position, which may present a collision riskto other neighboring hydrokinetic devices moored in an ocean currentfarm array. Further, the disappearance of the rotor drag force may alsocause a significant decrease in the drowning force and thus depthcontrol of the hydrokinetic device may become problematic, potentiallyleading to a rapid uncontrolled ascent or at least deviation from aspecified depth. Known tethered hydrokinetic devices have not generallybeen concerned with drag stabilization in the absence of rotoroperation.

Therefore, a solution is needed for the pitch and roll stabilization ofa tethered hydrokinetic device without the compromises to energyconversion performance of known devices. Further, a solution is neededto mimic or proxy the rotor drag in the absence of rotor operation toaid in depth control and avoid a rapid surge forward in the position ofthe device.

The present disclosure provides a hydrokinetic device that harnesses thekinetic energy of flowing water currents to provide clean, renewableenergy, as well as a system and a method for stabilizing the pitch, rolland drag of the hydrokinetic device.

SUMMARY OF THE DISCLOSURE

A method, a system, and a hydrokinetic device are provided forharnessing the kinetic energy of flowing water currents to provideclean, renewable energy, as well as a system and a method forstabilizing the pitch, roll and drag of the hydrokinetic device.

According to an aspect of the disclosure, a hydrokinetic device isdisclosed that extracts power from water current. The device comprises:a buoyant body; and a rotor coupled to the buoyant body configured todrive a power generator, wherein the buoyant body and the rotor jointlydefine a center of buoyancy and a center of gravity, the center ofbuoyancy being located above and upstream of the center of gravity. Thehydrokinetic device may further comprise: a moveable counterweight thatis configured to adjust the center of gravity; a variable ballast thatis configured to adjust the center of gravity; a hydroplane wing with anelevator control surface; or a keel that is attached to the buoyantbody, the keel comprising a deadweight attached to a distal end. Therotor may be configured to selectively engage or disengage a watercurrent flow.

According to a further aspect of the disclosure, a hydrokinetic deviceis disclosed that extracts power from water current, the devicecomprises: a buoyant body; a rotor coupled to the buoyant body, therotor being configured to drive a power generator; a keel coupled to thebuoyant body; and a deadweight coupled to a distal end of the keel. Thedevice may further comprise: a plurality of laterally separated ballasttanks that are configured to be alternately purged of water or filledwith water; a hydrodynamic lifting surface that is configured to providea rolling moment; a drag inducer that is configured to deploy a varyingdrag condition, wherein the varying drag condition comprises a high dragcondition, a low drag condition, or an intermediate drag condition; or adrag inducer that is configured to deploy a high drag condition, a lowdrag condition, or an intermediate drag condition. The deadweight may beoffset from a vertical plane of symmetry of the buoyant body. Thedeadweight may be movable between a fore position and an aft position,or between a port side position and a starboard side position.

According to a still further aspect of the disclosure, a hydrokineticdevice is disclosed that extracts power from water current. The devicecomprises: a buoyant body; a rotor coupled to the buoyant body, therotor being configured to drive a power generator; and a drag inducerthat is configured to deploy a varying drag condition, the varying dragcondition including a high drag condition, a low drag condition, or anintermediate drag condition. The device may further comprise: a keelthat is attached to the buoyant body, the keel comprising a deadweightattached to a distal end; a variable ballast that is configured toadjust the center of gravity; or a hydroplane wing with variableincidence means or an elevator control surface. The rotor may beconfigured to engage or disengage a water current flow. The drag inducermay be configured to disengage when the rotor is engaged. The draginducer may be further configured to engage when the rotor isdisengaged.

Additional features, advantages, and embodiments of the disclosure maybe set forth or apparent from consideration of the following detaileddescription and drawings. Moreover, it is to be understood that both theforegoing summary of the disclosure, the following detailed descriptionand drawings are exemplary and intended to provide further explanationwithout limiting the scope of the disclosure.

BRIEF DESCRIPTION OF THE EXHIBITS

The accompanying attachments, including drawings, which are included toprovide a further understanding of the disclosure, are incorporated inand constitute a part of this specification, illustrate embodiments ofthe disclosure and together with the detailed description serve toexplain the principles of the disclosure. No attempt is made to showstructural details of the disclosure in more detail than may benecessary for a fundamental understanding of the disclosure and thevarious ways in which it may be practiced. In the exhibits:

FIGS. 1A and 1B show perspective and side views, respectively, of anexample of a hydrokinetic device according to principles of thedisclosure;

FIG. 2A shows a side view of an example of a hydrokinetic device with acenter of buoyancy (CB) and center of gravity (CG) at about the samelongitudinal station;

FIG. 2B shows a side view of an example of a hydrokinetic device with aCB above the CG at the same longitudinal station;

FIG. 2C shows a side view of an example of a hydrokinetic device with aCB above and upstream of the CG;

FIG. 3A is a side view of an example of an ocean current farm array ofhydrokinetic devices with shallow mooring cable intercept angles;

FIG. 3B is a side view of an example of an ocean current farm array ofhydrokinetic devices with moderate mooring cable intercept angles;

FIG. 3C is a side view of an example of an ocean current farm array ofhydrokinetic devices with steep mooring cable intercept angles;

FIG. 4A is a side view of the hydrokinetic device of FIG. 1A with aballast and a counter-weight, wherein the CG of the hydrokinetic deviceis in an aft position;

FIG. 4B is a side view of the hydrokinetic device of FIG. 1A with aballast and a counter-weight, wherein the CG of the hydrokinetic deviceis a forward position;

FIG. 5A is a front view of the hydrokinetic device of FIG. 1A with arotor in an operational state and the hydrokinetic device rolled to astarboard side;

FIG. 5B is a front view of the hydrokinetic device of FIG. 1A with therotor in a non-operational state and the hydrokinetic device rolled to aport side with a keel weight located in a position transverse to thedevice plane of symmetry;

FIG. 5C is a front view of the hydrokinetic device of FIG. 1A with therotor in the operational state and the hydrokinetic device in a verticalorientation with the keel weight located in the position transverse tothe device plane of symmetry;

FIG. 6A is a perspective view of the hydrokinetic device of FIG. 1A,with a drag inducer deployed to a high drag condition;

FIG. 6B is a front view of the hydrokinetic device of FIG. 1A, with adrag inducer deployed to the high drag condition;

FIG. 7 is a side view of an ocean current farm array comprising aplurality of the hydrokinetic devices of FIG. 1A in various stages ofoperation; and

FIG. 8 shows an example of a process for detecting and controllingpitch, roll and drag of a hydrokinetic device, according to principlesof the disclosure.

The present disclosure is further described in the detailed descriptionthat follows.

DETAILED DESCRIPTION OF THE DISCLOSURE

The embodiments of the disclosure and the various features andadvantageous details thereof are explained more fully with reference tothe non-limiting embodiments and examples that are described and/orillustrated in the accompanying drawings and detailed in the followingdescription. It should be noted that the features illustrated in thedrawings are not necessarily drawn to scale, and features of oneembodiment may be employed with other embodiments as the skilled artisanwould recognize, even if not explicitly stated herein. Descriptions ofwell-known components and processing techniques may be omitted so as tonot unnecessarily obscure the embodiments of the disclosure. Theexamples used herein are intended merely to facilitate an understandingof ways in which the disclosure may be practiced and to further enablethose of skill in the art to practice the embodiments of the disclosure.Accordingly, the examples and embodiments herein should not be construedas limiting the scope of the disclosure, which is defined solely by theappended claims and applicable law. Moreover, it is noted that likereference numerals represent similar parts throughout the several viewsof the drawings.

A “computer”, as used in this disclosure, means any machine, device,circuit, component, or module, or any system of machines, devices,circuits, components, modules, or the like, which are capable ofmanipulating data according to one or more instructions, such as, forexample, without limitation, a processor, a microprocessor, a centralprocessing unit, a general purpose computer, a super computer, apersonal computer, a laptop computer, a palmtop computer, a notebookcomputer, a desktop computer, a workstation computer, a server, or thelike, or an array of processors, microprocessors, central processingunits, general purpose computers, super computers, personal computers,laptop computers, palmtop computers, notebook computers, desktopcomputers, workstation computers, servers, or the like. Further, thecomputer may include an electronic device configured to communicate overa communication link. The electronic device may include, for example,but is not limited to, a mobile telephone, a personal data assistant(PDA), a mobile computer, a stationary computer, a smart phone, mobilestation, user equipment, or the like.

A “network,” as used in this disclosure, means an arrangement of two ormore communication links. A network may include, for example, theInternet, a local area network (LAN), a wide area network (WAN), ametropolitan area network (MAN), a personal area network (PAN), a campusarea network, a corporate area network, a global area network (GAN), abroadband area network (BAN), any combination of the foregoing, or thelike. The network may be configured to communicate data via a wirelessand/or a wired communication medium. The network may include any one ormore of the following topologies, including, for example, apoint-to-point topology, a bus topology, a linear bus topology, adistributed bus topology, a star topology, an extended star topology, adistributed star topology, a ring topology, a mesh topology, a treetopology, or the like.

A “communication link”, as used in this disclosure, means a wired ,wireless and/or acoustic medium that conveys data or information betweenat least two points. The wired, wireless or acoustic medium may include,for example, a metallic conductor link, a radio frequency (RF)communication link, an Infrared (IR) communication link, an opticalcommunication link, or the like, without limitation. The RFcommunication link may include, for example, WiFi, WiMAX, IEEE 802.11,DECT, 0G, 1G, 2G, 3G or 4G cellular standards, Bluetooth, or the like.

The terms “including”, “comprising” and variations thereof, as used inthis disclosure, mean “including, but not limited to”, unless expresslyspecified otherwise.

The terms “a”, “an”, and “the”, as used in this disclosure, means “oneor more”, unless expressly specified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

Although process steps, method steps, algorithms, or the like, may bedescribed in a sequential order, such processes, methods and algorithmsmay be configured to work in alternate orders. In other words, anysequence or order of steps that may be described does not necessarilyindicate a requirement that the steps be performed in that order. Thesteps of the processes, methods or algorithms described herein may beperformed in any order practical. Further, some steps may be performedsimultaneously.

When a single device or article is described herein, it will be readilyapparent that more than one device or article may be used in place of asingle device or article. Similarly, where more than one device orarticle is described herein, it will be readily apparent that a singledevice or article may be used in place of the more than one device orarticle. The functionality or the features of a device may bealternatively embodied by one or more other devices which are notexplicitly described as having such functionality or features.

A “computer-readable medium”, as used in this disclosure, means anymedium that participates in providing data (for example, instructions)which may be read by a computer. Such a medium may take many forms,including non-volatile media, volatile media, and transmission media.Non-volatile media may include, for example, optical or magnetic disksand other persistent memory. Volatile media may include dynamic randomaccess memory (DRAM). Transmission media may include coaxial cables,copper wire and fiber optics, including the wires that comprise a systembus coupled to the processor. Transmission media may include or conveyacoustic waves, light waves and electromagnetic emissions, such as thosegenerated during radio frequency (RF) and infrared (IR) datacommunications. Common forms of computer-readable media include, forexample, a floppy disk, a flexible disk, hard disk, magnetic tape, anyother magnetic medium, a CD-ROM, DVD, any other optical medium, punchcards, paper tape, any other physical medium with patterns of holes, aRAM, a PROM, an EPROM, a FLASH-EEPROM, any other memory chip orcartridge, a carrier wave as described hereinafter, or any other mediumfrom which a computer can read.

Various forms of computer readable media may be involved in carryingsequences of instructions to a computer. For example, sequences ofinstruction (i) may be delivered from a RAM to a processor, (ii) may becarried over a wireless transmission medium, and/or (iii) may beformatted according to numerous formats, standards or protocols,including, for example, WiFi, WiMAX, IEEE 802.11, DECT, 0G, 1G, 2G, 3Gor 4G cellular standards, Bluetooth, or the like.

According to an aspect of the disclosure, a hydrokinetic device 100 isdisclosed that has a center of buoyancy (“CB”) above and upstream of thedevice's center of gravity (“CG”). The configuration of the hydrokineticdevice 100 provides a restoring pitching moment, which may be referredto as the body pitching moment. The body pitching moment opposes adrowning moment and maintains the hydrokinetic device 100 in a levelsteady state trimmed operational attitude with substantially zero furlangle, providing for maximum energy conversion performance. With theintroduction of the body pitching moment, the hydrokinetic device 100may be configured to include smaller or substantially nonexistent foreand/or aft lifting surfaces. Further, the hydrokinetic device 100 maysupport steeper mooring cable intercept angles with shorter, less costlyand lighter mooring cables, thereby allowing for deployment of largernumbers of hydrokinetic devices 100 per square kilometer and making moreefficient use of the natural resources. Additionally, the pitch attitudeof the hydrokinetic device 100 may be altered by moving counterweightsfore and aft, or by flooding and evacuating fore and aft ballast tanks,or by altering the lift or down-force on fore and aft hydrodynamicsurfaces.

According to a further aspect of the disclosure, a hydrokinetic device100 is disclosed that creates a rolling moment in opposition to theadverse torque created by an operational rotor. The hydrokinetic device100 may include a downwardly depending ventral keel structure with adead weight attached to a distal end to create the rolling moment. Inthis regard, the ventral keel acts as a weighted pendulum that, when aroll angle deflection occurs, the weighted ventral keel is angularlydisplaced in the direction of rotation of the rotor and passivelycreates a restoring rolling moment to rotate the entire hydrokineticdevice 100 back to a predetermined vertical orientation.

Additionally, the dead weight at the ventral keel distal end may beoffset from the vertical plane of symmetry of the hydrokinetic device100 such that when the rotor is in operation and rotor adverse torque ispresent, the ventral keel assumes a near vertical orientation; and, whenthe rotor is inoperative, the ventral keel assumes a slanted orangularly deflected orientation. The length of the ventral keel and theweight of the dead weight at the distant end may be configured so that aresulting opposing rolling moment substantially cancels any adversetorque created by the operational rotor.

According to a further aspect of the disclosure, a hydrokinetic device100 is disclosed that deploys or extends a rotor drag proxy device, ordrag inducer, in the absence of rotor operation to mimic the dragcreated by the operational rotor such that the upstream mooring cablesdo not slacken to a catenary condition causing the hydrokinetic deviceto surge forward in position and cause a collision or mooring cableentanglement risk to neighboring hydrokinetic devices that may be moorednearby in a patterned deployment farm array. In addition, the draginducer provides a means to modulate a drag force acting on hydrokineticdevice 100, thereby modulating the drowning force which may aide inmaintaining depth control in the absence of rotor operation.

FIG. 1A shows an example of a hydrokinetic device 100 configured inaccordance with the principles of the disclosure. FIG. 1B shows a sideview of the hydrokinetic device 100.

The hydrokinetic device 100 includes a hull 101, a rotor 109, an aftmounted electrical generator (not shown), a keel 105, a keel cylinder111, a hydrodynamic wing 106, and a harness 102. The hydrokinetic device100 may include a computer (not shown) and a transceiver (not shown).The hydrokinetic device 100 may include one or more sensors fordetecting ambient conditions, such as, for example, water temperature,pressure, depth, proximity of objects (such as, for example, of otherhydrokinetic devices, mammals, fish, vessels, and the like), speedand/or direction of water current flow, and the like. Further, the rotor109 may include an onboard hub controller (not shown) and a transceiver.The hull 101 may include a main pressure vessel which may provide themain source of buoyancy for the hydrokinetic device 100. Additionally,the hull 101 may include one or more interior ballast tanks (not shown)that can be alternately flooded or purged with water to adjust theweight (ballast), as well as the location of the center of gravity ofthe hydrokinetic device 100.

The rotor 109 may include a downstream horizontal axis rotor having aplurality of rotor blades 107 and a variable pitch control rotor hub108. The variable pitch control rotor hub 108 may be connected to theaft mounted electrical generator (not shown), which is employed in theproduction of electricity.

The keel 105 may include a ventral keel structure having, for example, amoveable counter weight (not shown) that is capable of fore and aftmovement. The keel 105 may be connected to the keel cylinder 111 andoffset by a distance 117 from a vertical plane of symmetry of thehydrokinetic device 100. The keel cylinder 111 may include a deadweight. The keel 105 and/or keel cylinder 111 may provide a variety ofpurposes, including, for example, a natural rudder for passive yawalignment, a weighted pendulum to aide in the cancellation of rotoradverse torque, a means to facilitate the CB above and upstream of theCG to facilitate production of the body pitching moment, a large surfacefor the mounting of one or more drag inducers 112 to facilitate dragmodulation, a leading edge root extension (LERX) 114 to provide aforward attachment point for the mooring system, and the like, and otheradvantageous uses as described herein, or that will become readilyapparent to one of ordinary skill in the art. The one or more drag proxydevices 112 may include, for example, split drag flaps. The hydrodynamicwing 106 may be generally mounted above the hull 101. Alternately, thehydrodynamic wing 106 may be mounted at par with the hull 101 or may bemounted below the hull 101. The LERX 14 may provide a nose-forwardattachment point for a harness 102. Alternately, the harness 102 may beattached to the hull 101.

The hydrodynamic wing 106 may be configured to provide either variableangle incidence deflections or trailing edge elevator control surfacedeflections to create lift or down-force on the hydrokinetic device 100.

The harness 102 may include a universal joint mooring device. Theharness 102 may be configured to allow the hydrokinetic device 100 tofreely pivot in both pitch and yaw, as seen, for example, in FIG. 1B,shown by an arrow 120. The harness 102 may be attached to one or moremooring cables 103. The mooring cables 103 may be attached to anchors104, which may be fixed to a surface 110, such as, for example, sea bed,a river bed, an underwater platform, and the like. The mooring cables103 may be arranged to prohibit port or starboard translational movementas the hydrokinetic device 100 yaws about the harness 102. The mooringcables 103 form an intercept angle 121 with the horizontal or transversecomponent of the water current flow vector C, shown in FIG. 1B.

The hydrokinetic device 100 is configured to be deployed in pattereneddeployment arrays, or ocean current farm arrays, (shown, for example, inFIGS. 3A-3C). Neighboring hydrokinetic devices 100 in a given farm arraymay share anchors 104. Electricity created by each onboard generator(not shown) may be routed to, for example, neighboring hydrokineticdevices 100 or one or more electric stations (not shown) located in thewater, or on land, to collect the electrical energy from eachhydrokinetic device 100 prior to transmitting the electricity to, forexample, a utility grid, which may be located on water or land. Theelectricity may be transmitted via electrical cables (not shown), whichmay be attached to, for example, the mooring cables 103 and routed tothe neighboring devices 100, or to the one or more stations.

The hydrokinetic device 100 is configured to maintain a fully levelsteady state trimmed operational attitude with a free-stream currentflowing in, for example, the direction shown by arrow C. In this regard,the hydrokinetic device 100 may maintain the rotational axis 115 ofrotor 109 substantially parallel to the oncoming free-stream currentflow C, thereby maximizing the conversion of the kinetic energy in themoving fluid to useable electrical power.

In the level steady state trimmed operational attitude, the hydrokineticdevice 100 may maintain the CB above and upstream of the CG to create abody pitching moment to oppose a drowning moment. Fore and aft ballasttanks (not shown) interior to the hull 101 may be purged or flooded withwater to alter the location of the CG relative to the location of the CBto adjust the magnitude of the body pitching moment to exactly cancelthe drowning moment, which may fluctuate from time to time with changingfree-stream current conditions. Further, a moveable counter weight, orkeel weight (not shown), located interior to the keel cylinder 111 maybe shifted fore and aft to alter the location of the CG relative to thelocation of the CB to also adjust the magnitude of the body pitchingmoment. Fore and aft trimming surfaces (not shown) may be used to trimout any excess pitching moments to remain in the level steady statetrimmed operational attitude.

The rotor 109 may be configured to rotate, for example, in the directionshown by arrow 116 in FIG. 1A about the rotational axis 115(counterclockwise as viewed from the front of the hydrokinetic device100). The rotation 116 of the rotor 109 creates a rolling moment oradverse torque that is imparted to the hydrokinetic device 100, which isalso in the direction of arrow 116. The rotor adverse torque may causethe keel 105 to angularly deflect to, for example, the port side,thereby causing the keel cylinder 111 (including, for example, a deadweight and counter weight contained therein) to traverse to the portside, thereby creating a restoring rolling moment to oppose the rotoradverse torque. As shown in FIG. 1A, the keel cylinder 111 may be offsetfrom the vertical plane of symmetry of the hydrokinetic device 100 bythe lateral distance 117.

The drag inducers 112 may include, for example, a pair of split dragflaps that are attached to the keel 105 near a trailing edge of the keel105, as seen in FIG. 1A. The drag inducers 112 may mimic and proxy adrag force of the rotor 109 in the absence of operation of the rotor109. To increase a drag force, the drag inducers 112 may be deflectedsubstantially simultaneously in opposite directions, as shown, forexample, in FIG. 6A. The drag inducers 112 may be progressivelydeflected, providing a progressively larger frontal area as the angle ofdeflection increases. To reduce a drag force, the drag inducers 112 maybe retracted inward and moved toward each other at substantially thesame time, providing a progressively smaller frontal area as the angleof deflection decreases. The drag inducers 112 may be deployed wheneverthe rotor 109 is not operating, or operating below a predeterminedthreshold, to prevent a surge forward in position of the hydrokineticdevice 100, or to control and/or maintain a specified depth.

The computer (not shown) in the hydrokinetic device 100 may beconfigured to control the various mechanical aspects of the hydrokineticdevice 100, according to the principles of the disclosure. The computermay control, for example, flooding or purging of water into the one ormore interior ballast tanks (not shown), the operation of the rotor 109,the rotor blade pitch angles associated with the variable pitch controlrotor hub 108, the operation of the drag inducers 112, the operation ofthe hydrodynamic wing 106, the trailing edge elevator control surfacedeflections, communication with the one or more stations (not shown)and/or power grid (not shown), the operation of the moveablecounterweight, or keel weight located interior to the keel cylinder 111,and the like. Communication between the onboard computer and, forexample, the station and/or grid may be carried out by means of theonboard transceiver (not shown) and communication links (not shown), asis known by those having ordinary skill in the art.

The station and/or grid may each include a computer (not shown) that iscommunicatively coupled via one or more transceivers, one or morecommunication links and, optionally, a network to a plurality ofhydrokinetic devices 100. The computer may be configured to remotelymonitor and control each of the hydrokinetic devices 100.

FIGS. 2A-2C show examples of three different hydrokinetic devices 200,220, and 240, each having a different configuration than the other two.In particular, FIG. 2A shows a side view of a hydrokinetic device 200with the center of buoyancy (CB) and center of gravity (CG) at about thesame longitudinal station. FIG. 2B shows a side view of a hydrokineticdevice 220 with a CB above the CG at the substantially the samelongitudinal station. FIG. 2C shows a side view of a hydrokinetic device240 with the CB above and upstream of the CG. FIGS. 2A-2C show somemechanical advantages gained by, for example, positioning the CB aboveand upstream of the CG.

FIG. 2A shows a hydrokinetic device 200 having a CB 219 and a CG 214co-located at substantially the same longitudinal and waterline station,having a near zero longitudinal separation 215. The hydrokinetic device200 may be restrained by a mooring cable 208. The mooring cable 208 mayhave, for example, a shallow intercept angle 207 with a horizontalreference plane. In this regard, the mooring cable 208 may transfer thevector forces 209, 210, 211 to the hydrokinetic device 200, includingthe drowning force 211.

Prior to the rotor 201 becoming operational, the hydrokinetic device 200may assume a level attitude (not shown). When the rotor 201 becomesoperational, the rotor 201 creates a large downstream drag force that isapplied to the hydrokinetic device 200, causing the hydrokinetic device200 to rotate nose down, as shown in FIG. 2A. The hydrokinetic device200 may rotate nose down until the drowning moment resulting from thedrowning force 211 of the hydrokinetic device 200 is substantially equaland opposite to the sum of a nose up moment caused by the wing 202 andthe nose up moment caused by the drag force of the rotor 201 actingabove the CG 214. The nose up moment caused by the wing 202 may beincreased by a trailing edge up angular deflection 212 by elevatorcontrol surface 203. As a result of this nose down rotation of thehydrokinetic device 200, a furl angle 206 is introduced with regard tothe rotational axis 204 of the rotor 201, thereby reducing the energyconversion performance by a factor approximately equal to a cube of thecosine of angle 206.

In order to return the hydrokinetic device 200 to a level trim attitude,the elevator control surface deflector 203 may be configured to deflecteven further trailing edge up to an angle 212, thereby increasing thedown-force on the wing 202 and causing a nose up moment of thehydrokinetic device 200. The resultant increased down-force on the wing202 may cause a trailing edge downwash flow angularity (or wake) todrift downstream and impinge onto the rotor 201, thereby causing therotor 201 to experience an apparent furl angle 212, which may be inaddition to the already existing geometric furl angle 206, both of whichconspire to degrade the energy conversion performance of rotor 201 At ashallow intercept angle 207, the mooring cables 208 must be lengthy,heavier and more costly.

At a steeper intercept angle 207, the magnitude of the drowning force211 will increase, thereby increasing the drowning moment acting onhydrokinetic device 200. With steeper intercept angle 207, the rotor 201will become increasingly furled, and less efficient, requiring a largerand more costly wing 202 to create the necessary restoring nose upmoments to level the hydrokinetic device 200. If the mooring cableattachment point were moved aft toward the CG 214 location in an attemptto reduce the drowning moment by shortening the lever arm associatedwith drowning force 211, the hydrokinetic device 200 may sacrificedirectional stability and the ability to align itself in yaw with theoncoming current direction.

FIG. 2B shows a hydrokinetic device 220 with a CB 239 and a CG 234 atsubstantially the same longitudinal station. However, the CB 239 islocated directly above the CG 234 when the hydrokinetic device 220 is ina substantially level trim attitude (not shown). The hydrokinetic device220 may be restrained by a mooring cable 228, which has a steeperintercept angle 227 with a horizontal reference plane than thehydrokinetic device 200 in FIG. 2A. The mooring cable 228 may transfervector forces 229, 230, 231 to the hydrokinetic device 220, includingthe drowning force 231, as shown in FIG. 2B.

Prior to the rotor 221 becoming operational, the hydrokinetic device 220may assume a level attitude (not shown). When the rotor 221 becomesoperational, it may create a large drag force downstream that causes thehydrokinetic device 220 to rotate nose down, as shown in FIG. 2B. As thehydrokinetic device 220 rotates nose down, the CB 239 advances upstreamof the CG 234. The nose down rotation of the hydrokinetic device 220 maystop when the drowning moment resulting from the drowning force 231 issubstantially equal and opposite to the sum of the nose up moment causedby a wing 222, the nose up moment caused by the rotor drag force of therotor 221 acting above the CG 234, and the nose up moment resulting froma longitudinal separation 235 between the CB 239 and the CG 234. Thenose up moment caused by the wing 222 may be aided by a trailing edge upangular deflection 232 by elevator control surface 223. The longitudinalseparation 235 may be solely a result of the nose down (or nose up)rotation of the hydrokinetic device 220. The CG 234 may have a heightseparation 236 with regard to the CB 239. With the additionalcontributing moment represented by the longitudinal separation 235between CG 234 and CB 239, a furl angle 226 (with regard to therotational axis 224 of the rotor 221) may be reduced relative to thefurl angle 206 shown in FIG. 2A.

In order to return the hydrokinetic device 220 to a level trim attitude,it may be necessary to increase the deflection angle 232 of the trailingedge elevator control surface 223, thereby introducing or increasingflow angularity into the downstream rotor 221. The flow angularity maycause the rotor 221 to experience an apparent furl angle 232 in additionto the previously described geometric furl angle 226, thereby reducingthe energy conversion efficiency of the rotor 221.

At a shallow intercept angle 227, mooring cable cables 228 must belengthy, more costly and heavier. At a steeper intercept angle 227, therotor 221 becomes even more furled and less efficient, requiring alarger, more costly wing 222 to create the necessary restoring nose upmoments to the hydrokinetic device 220. If the mooring cable attachmentpoint is moved aft toward the CG 234 location, in an effort to reducethe drowning moment by shortening the lever arm associated with drowningforce 231, the hydrokinetic device 220 may sacrifice directionalstability and the ability to align itself in yaw with the oncomingcurrent direction.

FIG. 2C shows an example of a hydrokinetic device 240 (or 100),according to principles of the disclosure. The hydrokinetic device 240has a CB 259 that may be located above and upstream of a CG 254 when thehydrokinetic device 240 is in a substantially level trim attitude. TheCG 254 may have a height separation 256 with regard to the CB 259. Thehydrokinetic device 240 may be restrained by a mooring cable 248, whichmay have a steeper intercept angle 247 (or 121 in FIG. 1B) than angles207 or 227 of FIGS. 2A, 2B, respectively. The mooring cable 248 maytransfer vector forces 249, 250, 251 to the hydrokinetic device 240,including a drowning force 251.

Prior to a rotor 241 (or 109) becoming operational, the hydrokineticdevice 240 may assume a nose high attitude (not shown), where the noseof the hydrokinetic device 240 is rotated upward and a separationdistance 255 between the CB 259 and CG 254 may be minimal. When therotor 241 becomes operational, it may create a large downstream dragforce that causes the hydrokinetic device 240 to rotate nose down from,for example, a nose high attitude. The hydrokinetic device 240 may ceaseto rotate nose down when the drowning moment resulting from drowningforce 251 becomes substantially equal and opposite to the sum of thenose up moment caused by the rotor drag force acting on the hydrokineticdevice 240 above the CG 254, and the body pitching moment resulting fromthe longitudinal separation 255 between the CB 259 and the CG 254. Bylocating the CB 259 above and upstream of the CG 254, the hydrokineticdevice 240 may remain in a substantially level steady state trimmedoperational attitude with a substantially zero geometric furl angle 246with regard to the rotational axis 244 of the rotor 241. Since atrimming moment will not be necessary from a wing 242 (or 106) andtrailing edge elevator control surface 243 may have zero deflectionangle 252, flow angularity may be avoided or minimized and, therefore,not introduced into the rotor 241. Accordingly, the rotor 241 may remainin its most efficient operating condition providing maximum energyconversion performance.

As seen in FIG. 2C, the intercept angle 247 can be significantly steeperthan the intercept angles 207, 227, shown in FIGS. 2A, 2B. Accordingly,the mooring cable 248 may be shorter, less costly and lighter than themooring cables 208, 228 in FIGS. 2A, 2B. The hydrokinetic device 240 isconfigured to offset the larger drowning moments conveyed from mooringcable 248 by adjusting the longitudinal separation 255 between CB 259and CG 254, without a loss in efficiency caused by a geometric orapparent furl angle of the rotor 241. Thus, energy conversionperformance of the rotor 241 may be maximized while simultaneouslyensuring pitch stability and a level trim operating attitude ofhydrokinetic device 240.

As noted earlier, the keel cylinder 260 (or 111) may include a movablecounterweight (not shown), and the hull 101 may include one or moreballast tanks (not tanks). By adjusting the counterweight in the keelcylinder 260 (for example, moving the counterweight fore or aft in thekeel cylinder 260) and/or exchanging water ballast between a pair offore and aft ballast tanks (in the hull 101), the position of the CG 254may be adjusted. Furthermore, by adjusting the counterweight in the keelcylinder 260 and exchanging the water ballast between the fore and aftballast thanks, the amount of longitudinal separation 255 between the CB259 and the CG 254 may be adjusted so that the hydrokinetic device 240remains in a level steady state trimmed operational attitude withsubstantially zero rotor furl angle 246 and substantially no liftingforce created by the wing 242 (or 106), thereby avoiding any geometricor apparent furl angle experienced by the rotor 241. Accordingly, thepitch of the hydrokinetic device 240 may be stabilized and a levelsteady state trimmed operational attitude maintained without comprisingthe energy conversion performance of the rotor 241.

According to an embodiment of the disclosure, the wing 242 (or 106) maybe eliminated entirely from the hydrokinetic device 240 (or 100). Inthis embodiment, pitch, roll and/or drag stabilization of the tetheredhydrokinetic device 240 may be accomplished by the remaining means.

According to another embodiment of the disclosure, the wing 242 (or 106)may be located proximate the CG 254 and thus may be used solely to liftor down-force (drown) the hydrokinetic device 240. Alternatively (oradditionally), the wing 242 may be located distant from CG 254 and maybe used as both a trimming device and a lifting device.

According to principles of the disclosure, the harness 102 may belocated reasonably far forward on the hydrokinetic device 240 tomaximize the directional stability and yaw alignment capability of thedevice. The body pitching moment resulting from the longitudinalseparation 255 of the CB 259 and CG 254 may assist in counter acting theincreased drowning moment resulting from the drowning force acting at areasonably far forward attachment point of the harness 102.

FIGS. 3A-3C show various examples of farm arrays of fully submergedoperational hydrokinetic devices 300, 310 and 320 with free-streamcurrent shown flowing in the direction of arrow C. In particular, FIG.3A shows a side view of an example of an ocean current farm array ofhydrokinetic devices 300 (or 200) with shallow mooring cable interceptangles 301 (or 207); FIG. 3B shows a side view of an example of an oceancurrent farm array of hydrokinetic devices 310 (or 220) with moderatemooring cable intercept angles 311 (or 227); and FIG. 3C shows a sideview of an example of an ocean current farm array of hydrokineticdevices 320 (or 240, or 100) with steep mooring cable intercept angles321 (or 121, or 247).

Referring to FIG. 3A, the hydrokinetic devices 300 generally correspondto the hydrokinetic device 200 shown in FIG. 2A. The hydrokineticdevices 300 are configured in a farm array, with each of thehydrokinetic devices 300 connected to a mooring cable having a shallowintercept angle 301. As seen in FIG. 3A, the shallow mooring cableintercept angles 301 require lengthy, costly and heavier mooring cables303 than the farm arrays shown in FIGS. 3B or 3C. Additionally, asignificant furl angle 305 may be introduced that causes a substantialreduction in energy conversion performance of the horizontal axis rotor.In addition to the increased cost and length of mooring cables 303, suchcables tend to be heavier, requiring a larger and costlier hydrodynamicdevice, buoyant volume, or larger wing lifting surface to support theincreased weight of the mooring cables 303.

A mooring overlap distance 302 denotes a distance between a location ofan upstream hydrokinetic device 300 and a surface bed anchoring location306 of the neighboring downstream hydrokinetic device 300. In order toincrease the density of hydrokinetic devices 300 within a patterneddeployment array of devices 300 and maximize the use of the naturalresource by using the smallest overall geographic footprint, mooringoverlap distances 302 may be increased so that successive rows ofdevices 300 in the downstream direction may be moved closer to theupstream row of devices 300. With lengthy mooring cables 303, it becomesmore problematic to increase the overlap distance 302 given, forexample, the possibility of mooring cable 303 entanglement, collisionsbetween neighboring devices 300, increased difficulty of servicing ananchoring location 316 or a mooring cable 303 of a hydrokinetic device300 that can only be accessed directly below an upstream neighboringoperational hydrokinetic device 300.

Referring to FIG. 3B, the hydrokinetic devices 310 generally correspondto the hydrokinetic device 220 shown in FIG. 2B. In the farm array ofhydrokinetic devices 310, a plurality of mooring cables 313 have steeperintercept angles 311 than the mooring cables 303 of the farm array shownin FIG. 3A. Accordingly, shorter, less costly and lighter mooring cables313 may be used compared to the mooring cables 303 of the farm arrayshown in FIG. 3A. The mooring cable overlap distance 312 may bedecreased compared to the overlap distance 302 of FIG. 3A, whilst stillincreasing the density of the hydrokinetic devices 310 in a givengeographic area.

Furthermore, while smaller than the furl angle 305 introduced in thehydrokinetic devices 300 in FIG. 3A, the hydrokinetic devices 310introduce a significant furl angle 315 that causes a substantialreduction in energy conversion performance of the horizontal axis rotor.

Referring to FIG. 3C, the hydrokinetic devices 320 generally correspondto the hydrokinetic device 240 shown in FIG. 2B, or the hydrokineticdevice 100 shown in FIGS. 1A, 1B. With the CB 259 above and upstream ofthe CG 254, as described in FIG. 2C, the hydrokinetic devices 320 mayuse the resultant body pitching moments to allow for the steepestmooring cable intercept angles 321, thereby allowing for the shortest,lightest and least costly cables 323, whilst allowing the hydrokineticdevices 320 to maintain a level steady state trimmed operationalattitude with substantially zero rotor furl angle 325 (geometric orapparent) that provides for maximum energy conversion performance.Furthermore, a greater number of hydrokinetic devices 320 may bedeployed in a smaller geographic area, thereby maximizing use of thenatural resource, while minimizing the mooring cable overlap distance322 between a location of an upstream hydrokinetic device 320 and asurface bed anchoring location 326 of the neighboring downstreamhydrokinetic device 300 to avoid cable entanglement risks andcomplications with servicing anchors or mooring cables of neighboringdevices 320.

FIG. 4A is a side view of a hydrokinetic device 400 that is similar to,or substantially the same as the hydrokinetic device 100 shown in FIG.1A, or the hydrokinetic device 240 shown in FIG. 2C. The hydrokineticdevice 400 includes at least two mechanisms for moving a CG 404 (or 254)fore and aft in relation to a CB 416 (or 259) to alter the magnitude ofa body pitching moment of the hydrokinetic device 400. For example, thehydrokinetic device 400 may include a pair of fore and aft locatedballast tanks 401, 402. As seen in FIG. 4A, the forward located ballasttank 401 is shown as being near-empty and the ballast tank 402 is shownas being near-full. The hydrokinetic device 400 may further include apump (not shown) that is configured to transfer water between the tanks401 and 402. The hydrokinetic device 400 may further include a movablecounterweight 403 in the keel cylinder 260 (or 111). The counterweight403 may be configured to move longitudinally along a length of the keelcylinder 260, from a fore to an aft position, or from an aft to a foreposition. The rotor axis is represented by 405.

The near-full aft ballast tank 402 and aft-most position of thecounterweight 403 in the hydrokinetic device 400 may be representativeof a maximum load condition. The maximum load condition may include, forexample, where the CG 254 is located in a most aft-location 404,corresponding to the largest magnitude of a resultant body pitchingmoment on the hydrokinetic device 400.

FIG. 4B is a side view of the hydrokinetic device 400 (represented by410) with a load condition where the CG 254 is located in a forward-mostlocation 414, corresponding to a minimum magnitude of the resultant bodypitching moment on the hydrokinetic device 400. As seen, thefore-located ballast tank 401 (represented by 411) is near-full and theaft-located ballast tank 402 (represented by 412) is near-empty.Further, the moveable counter weight 403 (represented by 413) ispositioned in a forward position. The ballast tanks 401, 402 and/or thecounterweight 403 may be employed to adjust the location of the CG 254and, thereby, change the magnitude of the body pitching moment of thehydrokinetic device 400 to maintain a substantially level steady statetrimmed operational attitude, so as to maximize energy conversionperformance by the alignment of the rotational axis of the rotor 241 (or109) and the free-stream current direction. The rotor axis isrepresented by 415.

FIG. 5A is a frontal view of the hydrokinetic device 500 that is similarto, or substantially the same as the hydrokinetic device 100 shown inFIG. 1A, or the hydrokinetic device 240 shown in FIG. 2C. Referring toFIG. 5A, the free-stream current C flows into the page with thehorizontal axis rotor 501 (or 109, or 241) rotating in, for example, acounterclockwise direction 502 about an axis of rotation, which isperpendicular to the surface of the page. The hydrokinetic device 500has a CB 259 (represented as 505) and a CG 254 (represented as 508).

During operation, the rotor 501 imparts a rolling moment, referred to asan adverse torque, to the hydrokinetic device 500 which tends to rollthe hydrokinetic device 500, for example, counterclockwise in thedirection 502. For example, the hydrokinetic device 500 may roll to abank angle 507, at which the adverse torque is substantially offset by arestoring rolling moment created by the weight of a deadweight 503and/or the counterweight 403 (represented by 503) acting thru a leverarm distance 506. The magnitude of the bank angle 507 is inverselyproportional to the length of the keel 105 (represented by 510), theweight of the deadweight 503, and/or the weight of the counterweight503. So, by using a longer keel 510, a heavier deadweight 503, and/or aheavier counterweight 503, a smaller bank angle 507 may be required tocreate the opposing rolling moment to offset the adverse torque createdby the operational rotor 501. Thus, the weighted keel 510 may act as arighting pendulum.

However, as seen in FIG. 5A, the hydrokinetic device 500 may beangularly displaced from a vertical reference plane 509, leaning, forexample, starboard and, therefore, not positioned in a preferred uprightvertical orientation. The preferred upright vertical orientation occurswhen the vertical plane of symmetry 504 of the hydrokinetic device 500coincides with the vertical reference plane 509. In order to provide therolling moment necessary to cancel the adverse torque from the rotor 501and simultaneously achieve the preferred upright vertical orientation ofthe hydrokinetic device 500, a keel weight 513 may be laterally offsetfrom the vertical plane of symmetry 504 of hydrokinetic device 500, asseen in FIG. 5B.

FIG. 5B is a front view of the hydrokinetic device 500, with the rotor501 in a non-operational condition and the hydrokinetic device 500rolled to a port side with a keel weight 513 located in a positiontransverse to the vertical plane of symmetry 504 of hydrokinetic device500 and attached to, or integrally formed with the keel 510. The keelweight 513 may be configured to be laterally offset from the verticalplane of symmetry 504 of the hydrokinetic device 500 by a distance 516.As seen in FIG. 5B, with the rotor 501 not operational, the hydrokineticdevice 500 will roll to the port side, thereby positioning a CB 515 anda CG 518 in vertical alignment with the vertical reference plane 509.

FIG. 5C is a front view of the hydrokinetic device 500 with the rotor501 in the operational state and the hydrokinetic device 500 in apreferred vertical orientation with the vertical plane of symmetry 504of hydrokinetic device 500 coincident with a vertical reference plane509. The keel weight 513 may be located in a position substantiallytransverse to the vertical plane of symmetry 504 of the hydrokineticdevice 500.

In FIG. 5C, with the rotor 501 operational and rotating in, for example,the direction 522, the hydrokinetic device 500 rolls to the starboardside from its prior port-side leaning position (shown in FIG. 5B),thereby righting the hydrokinetic device 500 to the preferred verticalorientation that is aligned with (or parallel to) the vertical referenceplane 509. In this operational condition, the CG 528 is laterallydisplaced and located to, for example, the port side of the CB 525,thereby creating a persistent rolling moment to oppose the adversetorque created by the operational rotor 501.

As seen in FIG. 5C, the hydrokinetic device 500 may include one or moredifferential control surface deflectors 533, which may be provided onthe wing 106 (represented as 531). The deflectors 533 may provideadditional righting moments that oppose the adverse torque due to theoperational rotor 501.

Further, the hydrokinetic device 500 may include a plurality of wingtanks 532 that may be attached to, or integrally formed with the wing531. The wing tanks 532 may be provided at the distal ends of the wing531 (for example, wing-tip tanks, shown in FIG. 5C), or at a positionlocated between the distal end of the wing 531 and the hull 101.Additional righting moments may be provided by alternate purging orflooding of the wing tanks 532 to oppose the adverse torque due to theoperational rotor 501.

Furthermore, the hydrokinetic device 500 may include a control surfacedeflector 535 that may be located on the distal end of the keel 524, asshown in FIG. 5C.

FIG. 6A shows a perspective view of a hydrokinetic device 600 that issimilar to, or substantially the same as the hydrokinetic device 100shown in FIG. 1A, or the hydrokinetic device 240 shown in FIG. 2C. InFIG. 6A, the hydrokinetic device 600 is shown with rotor blades 601 in afully feathered, non-operational condition and with the drag inducer 602located on the ventral keel 603 in a deflected position, therebycreating a high drag condition. The drag inducer 602 is shown asincluding, for example, a pair of split drag flaps.

FIG. 6B shows a front view of the hydrokinetic device 600, with the draginducer 602 deployed to a high drag condition. In FIG. 6B, the splitdrag flaps of the drag inducer 602 may be deflected to provide a largefrontal area, thereby imparting substantial drag under the force of thefree-stream current flow C.

The mooring cable drowning force is proportional to the magnitude of therotor drag force (for example, drowning force 251 in FIG. 2C).Accordingly, the presence or removal of the rotor drag force may causelarge changes in the magnitude of the mooring cable drowning force and,hence, alter the vertical force balance required to maintain a specifieddepth of operation of the hydrokinetic device 600. The drag inducer 602provides a proxy or substitute drag force for the rotor drag force,whenever the rotor drag force is absent or minimal. The drag inducer 602provides a proxy for rotor drag force that prevents large fore and aftmovement in position of the hydrokinetic device 600, which may occurduring the transition of rotor blade pitch angles from a rotoroperational condition to a rotor non-operational condition. Large foreand aft movements in position of the hydrokinetic device 600 may be veryproblematic, since the movements may slacken the upstream mooringcables, which may be of particular concern in a regularly spaced oceancurrent farm array where neighboring devices 600 may present a collisionrisk (see, for example, FIG. 7).

The drag inducer 602 may be deployed to a high drag condition anytimethe rotor is not operating, and retracted to a low drag or no dragcondition anytime the rotor is operational. Further, during a rotorblade 602 pitch angle engagement or disengagement sequence via, forexample, the use of a variable pitch control rotor hub, the drag inducer602 may retract or extend respectively in a manner and at a rate so asto keep the total drag force (or alternately total vertical force)acting on the hydrokinetic device 600 at a constant value, therebyproviding a seamless transition between rotor operational and rotornon-operational conditions.

The drag inducer 602 may include a variety of deployable high dragdevices, including, for example, the split drag flaps, deflectable bodyflaps or scales, deployable flaps located on wings or fore and afttrimming surfaces, pop-up or pop-out stall fences located on othersurfaces of the hydrokinetic device 600, wing or trimming surfacescapable of about 90 degree incidence deflections, a tethered ballute ora tethered parachute that may be ejected from an interior cavity of thehydrokinetic device 600, or other high drag deployable devices that maybe later retracted to a low drag or no drag condition.

FIG. 7 shows a side view of an ocean current farm array comprising aplurality of the hydrokinetic devices 700, 701, 702, 703 and 706 invarious stages of operation. Each of the hydrokinetic devices 700, 701,702, 703 and 706 may be similar to, or substantially the same as thehydrokinetic device 100 shown in FIG. 1A, or the hydrokinetic device 240shown in FIG. 2C. For illustration, the hydrokinetic devices 700, 701,702, 703 and 706 will be described below with reference to the exampleof the hydrokinetic device 100, shown in FIG. 1A.

The hydrokinetic devices 700, 701 and 702 may be operational in asubstantially level trim steady state, at a depth at which a rated speedmay occur and, thus, rated power may be produced by the onboardgenerators (not shown). The hydrokinetic device 703 may have its rotor109 disengaged and, for the sake of illustration, the drag inducer 112retracted to a non-drag, or low-drag condition. Accordingly, thehydrokinetic device 703 may be caused to surge forward in position withthe mooring cables 705 in a catenary condition and pose a collision riskto the immediate upstream neighboring hydrokinetic device 701. Bydeploying the drag inducer 112 to the high drag condition, thehydrokinetic device 703 will pull the mooring cables 705 taught andrecede downstream to a position 704, thereby alleviating any collisionrisk with the hydrokinetic device 701.

The hydrokinetic device 704 may have its rotor blades 107 fullyfeathered and its rotor 109 non-operational with the drag inducer 112deployed to a high drag condition, and with the aid of the down-force onits wing 106 and increased sea water in the ballast tanks (for example,401, 402 in FIG. 4A), the hydrokinetic device 704 may remain at thedepth at which the rated speed may occur whilst at an idle powercondition with the rotor non-operational (or substantiallynon-operational).

The hydrokinetic device 706 is shown in a semi-submerged surfacecondition, with its rotor 109 non-operational and the drag inducer 112deployed to an intermediate deflection angle, thus creating an amount ofdrag sufficient to draw the mooring cables 705 taught, but yet notenough drag to increase the drowning force to a level that would pullthe hydrokinetic device 706 to greater depths. In this condition, thehydrokinetic device 706 may be serviced and maintained by a crew from asurface vessel 707. In order to descend to an operating depth, thehydrokinetic device 706 may fully deploy the drag inducer 112 to a highdrag condition, thereby increasing the drowning force and pulling thedevice 706 below the water surface. Once below the surface, the wing 106may be rotated to negative incidence angles to create a down-force.Simultaneously (or at a different time), the ballast tanks (for example,shown in FIGS. 4A, 4B) may be filled with sea water to increase theweight of the hydrokinetic device 706 and descend the device 706 to aposition 708, having a depth at which the rated speed may occur. At thisdepth, a drag force transition may occur between the drag inducer 112that is progressively retracted towards the low drag condition and theactual rotor 109 now in the process of pitching the rotor blade pitchangles to an operational condition, thereby increasing the drag producedby the rotor 109 as it enters operation. This drag transition betweenrotor proxy (created by the drag inducer 112) and the actual rotor 109at the specified depth occurs such that the vertical force balanceacting on the entire hydrokinetic device 706 remains substantially zeroand the device, along with the aid of the wing 106 which is relievingdown-force as well as the ballast tanks 401, 402, which are offloadingballast during the rotor engagement transition process, remains at thespecified depth at the rated speed at which rated power may be generatedby hydrokinetic device 706. A similar but reverse drag force transitionmay occur as the rotor 109 is transitioned into a non-operationalcondition, wherein the drag force transference occurs from the rotor 109to the drag inducer 112 prior to a controlled ascent of the hydrokineticdevice 706. These two drag transition sequences, including, from a rotor109 operational condition to a rotor 109 non-operational condition, andfrom a rotor 109 non-operational condition back to a rotor 109operational condition, are referred to as a rotor disengage transitionprotocol and a rotor engage transition protocol, respectively, which aredescribed in co-pending U.S. patent application Ser. No. ______(Attorney Dkt. No. 2056997-5007US), filed on the same date as theinstant application, entitled POWER CONTROL PROTOCOL FOR A HYDROKINETICDEVICE INCLUDING AN ARRAY THEREOF, the entire disclosure of which ishereby incorporated herein by reference for all purposes as if fully setforth herein.

The hydrokinetic device 100 may be retained in the water by a mooringsystem, such as, for example, the mooring system described in co-pendingU.S. patent application Ser. No. ______ (Attorney Dkt. No.2056997-5006US), filed on the same date as the instant application, andentitled MOORING SYSTEM FOR A TETHERED HYDROKINETIC, the entiredisclosure of which is hereby incorporated herein by reference for allpurposes as if fully set forth herein.

The hydrokinetic device 100 may include a variable control rotor hubwith a self-contained energy storage reservoir, such as, for example,described in co-pending U.S. patent application Ser. No. ______(Attorney Dkt. No. 2056997-5005US), filed on the same date as theinstant application, and entitled VARIABLE CONTROL ROTOR HUB WITH SELFCONTAINED ENERGY STORAGE RESERVOIR, the entire disclosure of which ishereby incorporated herein by reference for all purposes as if fully setforth herein.

FIG. 8 shows an example of a process 800 for detecting and controllingpitch, roll and drag of a hydrokinetic device, according to principlesof the disclosure. Referring to FIGS. 1A and 8 concurrently, the process800 includes sensing and determining a pitch of the hydrokinetic device100 (Step 810), sensing and determining a roll (including verticalalignment) of the hydrokinetic device 100 (Step 814), and/or a dragforce of the hydrokinetic device 100 (Step 818).

If a determination is made that the pitch angle of the hydrokineticdevice 100 is outside of a predetermined range of pitch (YES at Step820), then the pitch angle of the hydrokinetic device 100 may beadjusted by, for example, controllably, alternately filling and purginga plurality of longitudinally separated ballast tanks with water untilthe pitch angle of the hydrokinetic device 100 is returned to thepredetermined range of pitch (Step 830), otherwise pitch angleadjustment is not carried out (NO at Step 820). Additionally (oralternatively), the pitch angle may be adjusted by controllably movingthe counterweight in the keel cylinder 111 until the pitch angle of thehydrokinetic device 100 is returned to the predetermined range of pitch(Step 830). Additionally (or alternatively), the pitch angle may bealtered by controllably adjusting portions of the hydrodynamic wing 106,including, for example, a variable incidence angle or one or moretrailing edges, until the pitch angle of the hydrokinetic device 100 isreturned to the predetermined range of pitch (Step 830).

If a determination is made that a vertical alignment position of thehydrokinetic device 100 is outside a predetermined range of verticalalignment positions (YES at Step 824), then the vertical alignment ofthe hydrokinetic device 100 may be adjusted by, for example, the methodsindicated in reference to FIG. 5C which may include additionally (oralternatively) filling and/or purging wing tanks 532, deflecting anelevator control surface 533 or deflecting a rudder control surface 535(Step 834), otherwise roll adjustment is not carried out (NO at Step824).

If a determination is made that a drag force of the hydrokinetic device100 is outside a predetermined range of drag force (YES at Step 828),then the drag of the hydrokinetic device 100 may be adjusted by, forexample, controllably retracting or deploying the drag inducer 112 untilthe aggregate of the drag force due to the rotor 109 and the drag forcedue to the drag created by the drag inducer 112 is within thepredetermined range of drag force (Step 838), otherwise drag adjustmentis not carried out (NO at Step 828). Additionally (or alternatively),the drag force acting on the hydrokinetic device 100 may be adjusted bychanges to the rotor blade 107 pitch angles, until the drag force isreturned to an acceptable range (YES step 828). The aggregate of thedrag force due to the rotor 109 and the drag force due to the dragcreated by the drag inducer 112 may be equal to the rotor drag forcecreated by the rotor 109 alone during normal operating conditions.

Although shown as being carried out at substantially the same time, thesensing and determining Steps 810 and 818 may be carried out atdifferent times. Similarly the decision Steps 820, 828, and theadjusting Steps 830, 838, may be carried out substantiallysimultaneously, or at different times.

According to an aspect of the disclosure, a computer readable medium maybe provided that includes a computer program with a plurality of codesections (or segments) tangibly embodied therein. The computer programmay include a code section for each of the Steps 810 through 838 in theprocess 800. When executed on, for example, the onboard computer (notshown) in the hydrokinetic device 100, the computer program may causedetection and control of pitch, roll and/or drag of the hydrokineticdevice 100.

In accordance with various embodiments of the present disclosure, themethods described herein are intended for operation as software programsrunning on a computer. Dedicated hardware implementations including, butnot limited to, application specific integrated circuits, programmablelogic arrays and other hardware devices can likewise be constructed toimplement the methods described herein. Furthermore, alternativesoftware implementations including, but not limited to, distributedprocessing or component/object distributed processing, parallelprocessing, or virtual machine processing can also be constructed toimplement the methods described herein.

Although the present specification describes components and functionsimplemented in the embodiments with reference to particular standardsand protocols, the disclosure is not limited to such standards andprotocols. Accordingly, replacement standards and protocols having thesame functions are considered equivalent.

While the disclosure has been described in terms of exemplaryembodiments, those skilled in the art will recognize that the disclosurecan be practiced with modifications in the spirit and scope of theappended claims. These examples given above are merely illustrative andare not meant to be an exhaustive list of all possible designs,embodiments, applications or modifications of the disclosure.

1. A hydrokinetic device for extracting power from water current, the device comprising: a buoyant body; and a rotor coupled to the buoyant body configured to drive a power generator, wherein the buoyant body and the rotor jointly define a center of buoyancy and a center of gravity, the center of buoyancy being located above and upstream of the center of gravity.
 2. The device according to claim 1, further comprising: a moveable counterweight that is configured to adjust the center of gravity.
 3. The device according to claim 1, further comprising: a variable ballast that is configured to adjust the center of gravity.
 4. The device according to claim 1, further comprising: a hydroplane wing with an elevator control surface.
 5. The device according to claim 1, further comprising: a keel that is attached to the buoyant body, the keel comprising a deadweight attached to a distal end.
 6. The device according to claim 1, wherein the rotor is configured to selectively engage or disengage a water current flow.
 7. A hydrokinetic device for extracting power from a water current, the device comprising: a buoyant body; a rotor coupled to the buoyant body, the rotor being configured to drive a power generator; a keel coupled to the buoyant body; and a deadweight coupled to a distal end of the keel.
 8. The device according to claim 7, wherein the deadweight is offset from a vertical plane of symmetry of the buoyant body.
 9. The device according to claim 7, wherein the deadweight is movable between a fore position and an aft position, or between a port side position and a starboard side position.
 10. The device according to claim 7, further comprising: a plurality of laterally separated ballast tanks that are configured to be alternately purged of water or filled with water.
 11. The device according to claim 7, further comprising: a hydrodynamic lifting surface that is configured to provide a rolling moment.
 12. The device according to claim 7, further comprising: a drag inducer that is configured to deploy a varying drag condition, wherein the varying drag condition comprises a high drag condition, a low drag condition, or an intermediate drag condition.
 13. The device according to claim 7, further comprising: a drag inducer that is configured to deploy a high drag condition, a low drag condition, or an intermediate drag condition.
 14. A hydrokinetic device for extracting power from a water current, the system comprising: a buoyant body; a rotor coupled to the buoyant body, the rotor being configured to drive a power generator; and a drag inducer that is configured to deploy a varying drag condition, the varying drag condition including a high drag condition, a low drag condition, or an intermediate drag condition.
 15. The device according to claim 14, wherein the rotor is configured to engage or disengage a water current flow.
 16. The device according to claim 14, wherein the drag inducer is configured to disengage when the rotor is engaged.
 17. The device according to claim 14, wherein the drag inducer is further configured to engage when the rotor is disengaged.
 18. The device according to claim 14, further comprising: a keel that is attached to the buoyant body, the keel comprising a deadweight attached to a distal end.
 19. The device according to claim 14, further comprising: a variable ballast that is configured to adjust the center of gravity.
 20. The device according to claim 14, further comprising: a hydroplane wing with variable incidence mechanism or an elevator control surface. 